1. Field of the Invention
The present invention relates to an operational amplifier operating on a low voltage.
2. Description of the Related Art
Electronic circuits of operational amplifiers and the like used for electronic devices are desired to always perform stable operations. For example, Patent Document 1 discloses an operational amplifier for controlling an offset voltage fluctuating in accordance with a change of a common-mode input voltage and reducing distortion of output.
In recent years, with the spread of downsized portable electronic device, electronic circuits have also been downsized and configured for low voltage consumption, so that such electronic circuits are desired to perform stable operations on a low power supply voltage.
For example, some operation amplifiers employ transistors with a low threshold. In accordance with this, even when the power supply voltage is lowered, the transistors operate within a saturation region. Thus, it is possible to realize an operational amplifier performing high-gain and stable operations on a low power supply voltage.
Further, Patent Document 2 discloses a CMOS input circuit having a low voltage rail-to-rail CMOS input stage, for example.
Patent Document 1: Japanese Laid-Open Patent Application No. 2001-339257
Patent Document 2: Japanese Laid-Open Patent Application No. 2001-274642
However, when the power supply voltage is further lowered in the above-mentioned conventional operational amplifiers, a circuit configuration thereof has a problem in that some transistors are incapable of performing operation within the saturation region due to different temperatures and processes.